1. Field of the Invention
The present invention relates to a solvent delivery pump for delivering a solvent by sliding a plunger in a pump head to repeat suctioning of the solvent from a suctioning port and discharge of the solvent from a discharge port.
2. Description of the Related Art
A general plunger-type solvent delivery pump will be described with reference to FIG. 2A.
A pump head 18 is mounted to a tip end of a pump body 2 with a cleaning chamber 12 interposed therebetween. A pump chamber 18a is provided in the pump head 18 and a plunger 3 is inserted into the pump chamber 18a. A base end portion of the plunger 3 is retained by a crosshead 4 housed in the pump body 2.
The crosshead 4 is driven for reciprocation in one direction (a left-right direction in the drawing) by a cam mechanism (not shown) and a tip end portion of the plunger 3 slides on a straight line in the pump chamber 18a in the pump head 18 as the crosshead 4 is driven for reciprocation. If the tip end portion of the plunger 3 slides on the straight line in the pump chamber 18a, a solvent is suctioned into the pump chamber 18a from a suctioning port 18b and is discharged from a discharge port 18c continuously to deliver the solvent.
To a portion of the pump chamber 18a where the plunger 3 is inserted, a plunger seal 20 for preventing leakage of the solvent from a clearance between an inner wall of the pump chamber 18a and an outer periphery of the plunger 3 is mounted. The plunger seal 20 is a ring-shaped member made of resin having a through hole in its central portion and retains, for sliding, the plunger 3 inserted through the through hole at the portion of the pump chamber 18a where the plunger 3 is inserted. In this manner, it is common practice in the plunger-type solvent delivery pump to mount the resin seal member to the portion of the pump chamber where the plunger is inserted (see Japanese Unexamined Patent Publication No. 2001-254686, for example).
The portion where the plunger seal 20 is mounted is shown in FIG. 2B. The plunger seal 20 has a cylindrical protruding portion 20a on its face (front face) on the pump chamber 18a side and the protruding portion 20a is fitted into a seal insertion portion 18d formed as a recessed portion in a face of the pump head 18 on the pump body 2 side. A backup ring 11 is disposed on a face (back face) of the plunger seal 20 on the pump body 2 side and biased toward the pump head 18 by a wall face of the cleaning chamber 12, and, as a result, a flange-shaped peripheral edge portion 20c of the plunger seal 20 is sandwiched between the pump head 18 and the backup ring 11.
In the example in FIG. 2B, the protruding portion 20a of the plunger seal 20 has an open groove 20b open on a front side so as to increase forces of the plunger seal 20 for retaining the plunger 3 and coming in close contact with a wall face of the pump head 18 by utilizing pressure from the pump chamber 18a, which improves sealing performance. The open groove 20b is a ring-shaped cavity surrounding the plunger 3 in a circumferential direction.
In the above solvent delivery pump, the flange-shaped peripheral edge portion 20c of the plunger seal 20 is sandwiched between the pump head 18 and the backup ring 11 and, therefore, it is necessary to provide a structure for allowing stress applied from the backup ring 11 on the plunger seal 20 to escape. Therefore, in some conventional cases, as in the example in FIG. 2B, an opening edge portion 18f of the seal insertion portion 18d of the pump head 18 is tapered and a base end portion 20d of the protruding portion 20a of the plunger seal 20 corresponding to the opening edge portion 18f is formed in a tapered shape corresponding to the tapered shape of the opening edge portion 18f. The tapered shape of the base end portion 20d of the protruding portion 20a is formed by a smaller face than the tapered shape of the opening edge portion 18f so as to form a clearance between the faces of both the tapered shapes for allowing the plunger seal 20 to be deformed due to the stress.
With this structure, however, edge portions of the tapered shape constantly come in contact with a surface of the plunger seal 20, the stress for fixing the plunger seal 20 is concentrated on these portions, and these portions are more likely to deteriorate than other portions. If the plunger seal 20 deteriorates and the performance for sealing the portion of the pump chamber 18a where the plunger 3 is inserted reduces, the solvent leaks from the pump chamber 18a to the pump body 2 side, and it is impossible to deliver the solvent with high accuracy.